The present invention generally relates to fuel-fired heating appliances, such as water heaters and, in a preferred embodiment thereof, more particularly relates to a gas-fired water heater having incorporated therein a specially designed flammable vapor sensor-based burner shut-off system.
Gas-fired residential and commercial water heaters are generally formed to include a vertical cylindrical water storage tank with a gas burner structure, typically comprising a main burner and an associated pilot burner, disposed in a combustion chamber below the tank. The burner is supplied with a fuel gas through a gas supply line, and combustion air through one or more air inlet passages providing communication between ambient air and the interior of the combustion chamber.
Water heaters of this general type are extremely safe in operation. However, when gasoline or other flammable liquids are stored or used improperly in proximity to the water heater, there may exist a possibility of flammable vapors becoming entrained in the air intake of the water heater. It is theorized that such vapors might cause secondary combustion to occur within the confines of the water heater combustion chamber. It is accordingly possible for the resulting flame to propagate out of the combustion chamber into the ambient environment around the water heater as a result of following the intake path of the flammable vapor.
In view of this, various modern gas-fired water heater designs, as well as the designs of other types of fuel-fired heating appliances, focus upon the inhibition and/or control of the entrance of flammable vapors into a combustion chamber of the appliance. It is to this design goal that the present invention is directed.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, fuel-fired heating apparatus, representatively a gas-fired water heater, is provided with a specially designed flammable vapor sensor-based burner shutoff system.
A gas-fired water heater illustratively embodying principles of the present invention may be either a power vented or natural draft type and is restable on a horizontal support surface such as a floor. In a representative preferred embodiment thereof, the gas-fired water heater includes a tank adapted to hold a quantity of water, a combustion chamber disposed beneath the tank, and a flue communicated with the interior of the combustion chamber and extending upwardly through the interior of the tank. A gas burner and an associated pilot device are disposed within the combustion chamber, with the burner being operable to receive gas from a source thereof and combust a gas/air mixture within the combustion chamber. A control system is provided and is operable to disable the burner and associated pilot device in response to receipt of a shutdown signal.
A combustion air inlet passage is provided and is operative to deliver combustion air to the combustion chamber. The combustion air inlet passage has an inlet portion exposed to ambient air adjacent the gas fired water heater, and combustion air is deliverable to the combustion chamber only via such inlet portion and through the combustion air inlet passage.
Also incorporated in the gas-fired water heater is a flammable vapor sensor which is disposed externally of the combustion air inlet passage, at an elevation lower than that of its inlet portion, and being operative to sense flammable vapor, illustratively hydrocarbon fumes, and responsively transmit the shutdown signal to the control system which, in turn, operates to disable the burner and associated pilot device.
The elevation of the combustion air passage inlet portion relative to the flammable vapor sensor uniquely creates a time delay between the time at which the sensor is exposed to flammable vapor created at floor level by, for example a spill of flammable liquid adjacent the water heater, and the time at which flammable vapor reaches the elevated combustion air passage inlet portion to enable the flammable vapor to traverse the combustion air passage and enter the combustion chamber. This time delay gives the sensor, and the associated burner control system, additional time to sense the flammable vapor and disable the burner and pilot device before a combustible concentration of flammable vapors enters the combustion chamber.
Illustratively, the combustion chamber has a perforated bottom side wall portion with openings therein through which combustion air may enter the combustion chamber. The openings are preferably spaced and configured to (1) allow combustion air to flow upwardly through the openings with a pressure drop which is sufficiently low so as to not materially impede the combustion process of the water heater, and (2) act as flame arresting passages that hinder a downward flow of flames through the openings in the event that flammable vapor passes upwardly through the openings into the combustion chamber are ignited within the combustion chamber.
In an illustrated preferred embodiment of the gas-fired water heater, the combustion air passage is at least partially defined by an external wall structure having a vertical portion in which the elevated combustion air passage inlet portion is formed, and a horizontal portion extending beneath the combustion chamber and having an interior communicated with the interior of the combustion chamber. As will be readily appreciated by those of skill in this particular art, however, a variety of other techniques could alternatively be employed to elevate the water heater""s combustion air intake location relative to the flammable vapor sensor to provide a time delay between the sensor""s exposure to flammable vapors and potential entry of such flammable vapors into the combustion chamber.
While principles of the present invention are illustrated herein as being representatively incorporated in a fuel-fired water heater, it will be readily appreciated by those of ordinary skill in this particular art that such principles are not limited to a water heater, but could be alternatively incorporated to advantage in a variety of other types of fuel-fired heating appliances including, but not limited to, boilers and air heating furnaces.